This invention generally relates to the electric lamp art and has particular reference to a low-pressure discharge lamp and ballast unit that is adapted for use as a replacement for an incandescent-type lamp bulb in various kinds of lighting fixtures such as table lamps and the like.
Compact fluorescent lamps having plug-in type ballast and adapter components which provide a lamp assembly that can be used as a substitute for an incandescent lamp in the screw sockets of conventional lighting fixtures are generally well known in the art. A fluorescent lamp assembly having these features is disclosed in U.S. Pat. No. 3,551,736 issued Dec. 29, 1970 to Doehner. As shown in FIGS. 1, 2, 4 and 6 of this patent, the plug-in ballast component contains a single iron-core inductive ballast that is of annular shape and is housed in a cylindrical module that matches the contour of the tubular fluorescent lamp. Another screw-in type fluorescent lamp assembly which is designed for use in fixtures intended for incandescent lamp bulbs is disclosed in U.S. Pat. No. 3,953,761 issued Apr. 27, 1976 to Giudice. In accordance with this patent the fluorescent lamp is of such construction that it defines a central cavity or chamber which receives an axially-elongated inductive ballast component. In U.S. Pat. No. 3,815,080 (issued June 4, 1974 to Summa) a conventional double-ended fluorescent lamp is coupled to a threaded base member by plug-in adapters to provide an elongated screw-in type lamp assembly.
Compact fluorescent lamp units which comprise a partitioned fluorescent lamp of single-ended construction having pin contacts that are plugged into a ballast module which also contains a DC-operating circuit means and has a threaded base member which permits the lamp unit to be used in screw type sockets are also known and are disclosed in U.S. Pat. No. 4,173,730 issued Nov. 6, 1979 to Young et al. Fluorescent luminaires having lamp components of triple-U-bent or "double-fold" configuration that are mounted on cylindrical-shaped modules which contain a ballast component and have blade-like or screw type connectors are disclosed in Japanese Design Patents No. 437,859 of Takeda et al. granted on applications Showa No. 49-28293 and Showa No. 49-28295 filed Aug. 16, 1974.
While the prior art screw-in fluorescent lamp units were satisfactory from the standpoint of providing an energy-efficient substitute for incandescent lamps, the construction and size of the ballast module placed dimensional constraints on the fluorescent lamp component which reduced its size and thus its light output. The stringent size limitations on the lamp component derived from the fact that the lamp unit had to be small enough to fit within the harp components that are conventionally used in table-lamp fixtures and the like to hold the lamp shades in place. Since the light output of a fluorescent lamp is principally determined by the length of its arc path (and hence the physical dimensions of the lamp envelope), it was very difficult in the prior art to provide a fluorescent lamp-ballast unit that was not only compact enough to fit into table-lamp fixtures and the like but would also generate enough light to match the illumination level of the incandescent lamps normally used in such fixtures.